1. Fundamentals of Multimedia 2 nd ed., Chapter 5 Li, Drew, Liu1 Chapter 5 Fundamental Concepts in Video 5.1 Analog Video 5.2 Digital Video 5.3 Video Display Interfaces 5.4 3D Video and TV

2. Fundamentals of Multimedia 2 nd ed., Chapter 5 5.1 Analog Video An analog signal f ( t ) samples a time-varying image. So- called “progressive” scanning traces through a complete picture (a frame) row-wise for each time interval. In TV, and in some monitors and multimedia standards as well, another system, called “interlaced” scanning is used: a)The odd-numbered lines are traced first, and then the even- numbered lines are traced. This results in “odd” and “even” fields — two fields make up one frame. b)In fact, the odd lines (starting from 1) end up at the middle of a line at the end of the odd field, and the even scan starts at a half-way point. 2Li, Drew, Liu

3. Fundamentals of Multimedia 2 nd ed., Chapter 5 Fig. 5.1: Interlaced raster scan c) Figure 5.1 shows the scheme used. First the solid (odd) lines are traced, P to Q, then R to S, etc., ending at T; then the even field starts at U and ends at V. d) The jump from Q to R, etc. in Figure 5.1 is called the horizontal retrace, during which the electronic beam in the CRT is blanked. The jump from T to U or V to P is called the vertical retrace. 3Li, Drew, Liu

4. Fundamentals of Multimedia 2 nd ed., Chapter 5 Because of interlacing, the odd and even lines are displaced in time from each other — generally not noticeable except when very fast action is taking place on screen, when blurring may occur. For example, in the video in Fig. 5.2, the moving helicopter is blurred more than is the still background. 4Li, Drew, Liu

5. Fundamentals of Multimedia 2 nd ed., Chapter 5 Fig. 5.2: Interlaced scan produces two fields for each frame. (a) The video frame, (b) Field 1, (c) Field 2, (d) Difference of Fields (a) (b)(c)(d) 5Li, Drew, Liu

6. Fundamentals of Multimedia 2 nd ed., Chapter 5 Since it is sometimes necessary to change the frame rate, resize, or even produce stills from an interlaced source video, various schemes are used to “de-interlace” it. a)The simplest de-interlacing method consists of discarding one field and duplicating the scan lines of the other field. The information in one field is lost completely using this simple technique. b)Other more complicated methods that retain information from both fields are also possible. Analog video use a small voltage offset from zero to indicate “black”, and another value such as zero to indicate the start of a line. For example, we could use a “blacker- than-black” zero signal to indicate the beginning of a line. 6Li, Drew, Liu

7. Fundamentals of Multimedia 2 nd ed., Chapter 5 Fig. 5.3: Electronic signal for one NTSC scan line. 7Li, Drew, Liu

8. Fundamentals of Multimedia 2 nd ed., Chapter 5 5.1.1 NTSC Video NTSC (National Television System Committee) TV standard is mostly used in North America and Japan. It uses the familiar 4:3 aspect ratio (i.e., the ratio of picture width to its height) and uses 525 scan lines per frame at 30 frames per second (fps). a)NTSC follows the interlaced scanning system, and each frame is divided into two fields, with 262.5 lines/field. b)Thus the horizontal sweep frequency is 525×29.97 ≈ 15, 734 lines/sec, so that each line is swept out in 1/15.734 × 103 sec ≈ 63.6μsec. c)Since the horizontal retrace takes 10.9 μsec, this leaves 52.7 μsec for the active line signal during which image data is displayed (see Fig.5.3). 8Li, Drew, Liu

9. Fundamentals of Multimedia 2 nd ed., Chapter 5 Fig. 5.4 shows the effect of “vertical retrace & sync” and “horizontal retrace & sync” on the NTSC video raster. Fig. 5.4: Video raster, including retrace and sync data 9Li, Drew, Liu

10. Fundamentals of Multimedia 2 nd ed., Chapter 5 a)Vertical retrace takes place during 20 lines reserved for control information at the beginning of each field. Hence, the number of active video lines per frame is only 485. b)Similarly, almost 1/6 of the raster at the left side is blanked for horizontal retrace and sync. The non-blanking pixels are called active pixels. c)Since the horizontal retrace takes 10.9 μsec, this leaves 52.7 μsec for the active line signal during which image data is displayed (see Fig.5.3). d)It is known that pixels often fall in-between the scan lines. Therefore, even with non-interlaced scan, NTSC TV is only capable of showing about 340 (visually distinct) lines, i.e., about 70% of the 485 specified active lines. With interlaced scan, this could be as low as 50%. 10Li, Drew, Liu

11. Fundamentals of Multimedia 2 nd ed., Chapter 5 NTSC video is an analog signal with no fixed horizontal resolution. Therefore one must decide how many times to sample the signal for display: each sample corresponds to one pixel output. A “pixel clock” is used to divide each horizontal line of video into samples. The higher the frequency of the pixel clock, the more samples per line there are. Different video formats provide different numbers of samples per line, as listed in Table 5.1. Table 5.1: Samples per line for various video formats FormatSamples per line VHS240 S-VHS400-425 Betamax500 Standard 8 m300 Hi-8 mm425 11Li, Drew, Liu

12. Fundamentals of Multimedia 2 nd ed., Chapter 5 Color Model and Modulation of NTSC NTSC uses the YIQ color model, and the technique of quadrature modulation is employed to combine (the spectrally overlapped part of) I (in-phase) and Q (quadrature) signals into a single chroma signal C : C = I cos(F sc t) + Qsin(F sc t) (5.1) This modulated chroma signal is also known as the color subcarrier, whose magnitude is, and phase is tan −1 ( Q / I ). The frequency of C is F sc ≈ 3.58 MHz. The NTSC composite signal is a further composition of the luminance signal Y and the chroma signal as defined below: composite = Y +C = Y +Icos(F sc t) + Qsin(F sc t) (5.2) 12Li, Drew, Liu

13. Fundamentals of Multimedia 2 nd ed., Chapter 5 Fig. 5.5: NTSC assigns a bandwidth of 4.2 MHz to Y, and only 1.6 MHz to I and 0.6 MHz to Q due to human insensitivity to color details (high frequency color changes). 13Li, Drew, Liu Fig. 5.5: Interleaving Y and C signals in the NTSC spectrum.

14. Fundamentals of Multimedia 2 nd ed., Chapter 5 Decoding NTSC Signals The first step in decoding the composite signal at the receiver side is the separation of Y and C. After the separation of Y using a low-pass filter, the chroma signal C can be demodulated to extract the components I and Q separately. To extract I : 1.Multiply the signal C by 2cos ( F sc t ), i.e., 14Li, Drew, Liu

15. Fundamentals of Multimedia 2 nd ed., Chapter 5 2)Apply a low-pass filter to obtain I and discard the two higher frequency (2 F sc ) terms. Similarly, Q can be extracted by first multiplying C by 2sin(F sc t) and then low-pass filtering. 15Li, Drew, Liu

16. Fundamentals of Multimedia 2 nd ed., Chapter 5 The NTSC bandwidth of 6 MHz is tight. Its audio subcarrier frequency is 4.5 MHz. The Picture carrier is at 1.25 MHz, which places the center of the audio band at 1.25+4.5 = 5.75 MHz in the channel (Fig. 5.5). But notice that the color is placed at 1.25+3.58 = 4.83 MHz. 16Li, Drew, Liu

17. Fundamentals of Multimedia 2 nd ed., Chapter 5 So the audio is a bit too close to the color subcarrier — a cause for potential interference between the audio and color signals. It was largely due to this reason that the NTSC color TV actually slowed down its frame rate to 30×1,000/1,001 ≈ 29.97 fps. As a result, the adopted NTSC color subcarrier frequency is slightly lowered to f sc = 30 × 1,000/1,001 × 525 × 227.5 ≈ 3.579545 MHz, ** 227.5 is the # of color samples per scan line in NTSC broadcast TV. Li, Drew, Liu17

18. Fundamentals of Multimedia 2 nd ed., Chapter 5 5.1.2 PAL Video PAL (Phase Alternating Line) is a TV standard widely used in Western Europe, China, India, and many other parts of the world. PAL uses 625 scan lines per frame, at 25 frames/second, with a 4:3 aspect ratio and interlaced fields. (a)PAL uses the YUV color model. It uses an 8 MHz channel and allocates a bandwidth of 5.5 MHz to Y, and 1.8 MHz each to U and V. The color subcarrier frequency is f sc ≈ 4.43 MHz. Li, Drew, Liu18

19. Fundamentals of Multimedia 2 nd ed., Chapter 5 (a)In order to improve picture quality, chroma signals have alternate signs (e.g., +U and -U) in successive scan lines, hence the name “Phase Alternating Line”. (b)This facilitates the use of a (line rate) comb filter at the receiver — the signals in consecutive lines are averaged so as to cancel the chroma signals (that always carry opposite signs) for separating Y and C and obtaining high quality Y signals. Li, Drew, Liu19

20. Fundamentals of Multimedia 2 nd ed., Chapter 5 5.1.3 SECAM Video SECAM stands for Système Electronique Couleur Avec Mémoire, the third major broadcast TV standard. SECAM also uses 625 scan lines per frame, at 25 frames per second, with a 4:3 aspect ratio and interlaced fields. SECAM and PAL are very similar. They differ slightly in their color coding scheme: (a)In SECAM, U and V signals are modulated using separate color subcarriers at 4.25 MHz and 4.41 MHz respectively. (b)They are sent in alternate lines, i.e., only one of the U or V signals will be sent on each scan line. Li, Drew, Liu20

21. Fundamentals of Multimedia 2 nd ed., Chapter 5 Table 5.2 gives a comparison of the three major analog broadcast TV systems. Table 5.2: Comparison of Analog Broadcast TV Systems 21Li, Drew, Liu TV System Fram e Rate (fps) # of Scan Lines Total Channel Width (MHz) Bandwidth Allocation (MHz) YI or UQ or V NTSC29.975256.04.21.60.6 PAL256258.05.51.8 SECAM256258.06.02.0

22. Fundamentals of Multimedia 2 nd ed., Chapter 5 5.2 Digital Video The advantages of digital representation for video are many. For example: (a)Video can be stored on digital devices or in memory, ready to be processed (noise removal, cut and paste, etc.), and integrated to various multimedia applications; (b)Direct access is possible, which makes nonlinear video editing achievable as a simple, rather than a complex, task; (c)Repeated recording does not degrade image quality; (d)Ease of encryption and better tolerance to channel noise. Li, Drew, Liu22

23. Fundamentals of Multimedia 2 nd ed., Chapter 5 5.2.1 Chroma Subsampling Since humans see color with much less spatial resolution than they see black and white, it makes sense to “decimate” the chrominance signal. Interesting (but not necessarily informative!) names have arisen to label the different schemes used. To begin with, numbers are given stating how many pixel values, per four original pixels, are actually sent: a)The chroma subsampling scheme “4:4:4” indicates that no chroma subsampling is used: each pixel’s Y, Cb and Cr values are transmitted, 4 for each of Y, Cb, Cr. Li, Drew, Liu23

24. Fundamentals of Multimedia 2 nd ed., Chapter 5 b)The scheme “4:2:2” indicates horizontal subsampling of the Cb, Cr signals by a factor of 2. That is, of four pixels horizontally labelled as 0 to 3, all four Ys are sent, and every two Cb’s and two Cr’s are sent, as (Cb0, Y0)(Cr0, Y1)(Cb2, Y2)(Cr2, Y3)(Cb4, Y4), and so on (or averaging is used). c)The scheme “4:1:1” subsamples horizontally by a factor of 4. d)The scheme “4:2:0” subsamples in both the horizontal and vertical dimensions by a factor of 2. Theoretically, an average chroma pixel is positioned between the rows and columns as shown Fig.5.6. Scheme 4:2:0 along with other schemes is commonly used in JPEG and MPEG (see later chapters in Part 2). 24Li, Drew, Liu

25. Fundamentals of Multimedia 2 nd ed., Chapter 5 Fig. 5.6: Chroma subsampling 25Li, Drew, Liu

26. Fundamentals of Multimedia 2 nd ed., Chapter 5 5.2.2 CCIR and ITU-R Standards for Digital Video CCIR is the Consultative Committee for International Radio, and one of the most important standards it has produced is CCIR-601, for component digital video. – This standard has since become standard ITU-R-601, an international standard for professional video applications — adopted by certain digital video formats including the popular DV video. Table 5.3 shows some of the digital video specifications, all with an aspect ratio of 4:3. The CCIR 601 standard uses an interlaced scan, so each field has only half as much vertical resolution (e.g., 240 lines in NTSC). Li, Drew, Liu26

27. Fundamentals of Multimedia 2 nd ed., Chapter 5 CIF stands for Common Intermediate Format specified by the CCITT. (a)The idea of CIF is to specify a format for lower bitrate. (b)CIF is about the same as VHS quality. It uses a progressive (non-interlaced) scan. (c)QCIF stands for “Quarter-CIF”. All the CIF/QCIF resolutions are evenly divisible by 8, and all except 88 are divisible by 16; this provides convenience for block-based video coding in H.261 and H.263, discussed later in Chapter 10. 27Li, Drew, Liu

28. Fundamentals of Multimedia 2 nd ed., Chapter 5 a)Note, CIF is a compromise of NTSC and PAL in that it adopts the ‘NTSC frame rate and half of the number of active lines as in PAL. Table 5.3: ITU-R digital video specifications 28Li, Drew, Liu CCIR 601 525/60 NTSC CCIR 601 625/50 PAL/SECA M CIFQCIF Luminance resolution720 x 480720 x 576352 x 288176 x 144 Chrominance resolution 360 x 480360 x 576176 x 14488 x 72 Colour Subsampling4:2:2 4:2:0 Fields/sec605030 InterlacedYes No

29. Fundamentals of Multimedia 2 nd ed., Chapter 5 5.2.3 High Definition TV (HDTV) The main thrust of HDTV (High Definition TV) is not to increase the “definition” in each unit area, but rather to increase the visual field especially in its width. a)The first generation of HDTV was based on an analog technology developed by Sony and NHK in Japan in the late 1970s. b)MUSE (MUltiple sub-Nyquist Sampling Encoding) was an improved NHK HDTV with hybrid analog/digital technologies that was put in use in the 1990s. It has 1,125 scan lines, interlaced (60 fields per second), and 16:9 aspect ratio. Li, Drew, Liu29

30. Fundamentals of Multimedia 2 nd ed., Chapter 5 a)Since uncompressed HDTV will easily demand more than 20 MHz bandwidth, which will not fit in the current 6 MHz or 8 MHz channels, various compression techniques are being investigated. b)It is also anticipated that high quality HDTV signals will be transmitted using more than one channel even after compression. Li, Drew, Liu30

31. Fundamentals of Multimedia 2 nd ed., Chapter 5 A brief history of HDTV evolution: -In 1987, the FCC decided that HDTV standards must be compatible with the existing NTSC standard and be confined to the existing VHF (Very High Frequency) and UHF (Ultra High Frequency) bands. -In 1990, the FCC announced a very different initiative, i.e., its preference for a full-resolution HDTV, and it was decided that HDTV would be simultaneously broadcast with the existing NTSC TV and eventually replace it. -Witnessing a boom of proposals for digital HDTV, the FCC made a key decision to go all-digital in 1993. A “grand alliance” was formed that included four main proposals, by General Instruments, MIT, Zenith, and AT&T, and by Thomson, Philips, Sarnoff and others. -This eventually led to the formation of the ATSC (Advanced Television Systems Committee) — responsible for the standard for TV broadcasting of HDTV. -In 1995 the U.S. FCC Advisory Committee on Advanced Television Service recommended that the ATSC Digital Television Standard be adopted. 31Li, Drew, Liu

32. Fundamentals of Multimedia 2 nd ed., Chapter 5 The standard supports video scanning formats shown in Table 5.4. In the table, “I” mean interlaced scan and “P” means progressive (non-interlaced) scan. Table 5.4: Advanced Digital TV formats supported by ATSC 32Li, Drew, Liu # of Active Pixels per line # of Active Lines Aspect Ratio Picture Rate 1,9201,08016:960P 60I 30P 24P 1,28072016:960P 30P 24P 70448016:9 or 4:360P 60I 30P 24P 6404804:360P 60I 30P 24P

33. Fundamentals of Multimedia 2 nd ed., Chapter 5 For video, MPEG-2 is chosen as the compression standard. For audio, AC-3 is the standard. It supports the so-called 5.1 channel Dolby surround sound, i.e., five surround channels plus a subwoofer channel. The salient difference between conventional TV and HDTV: a)HDTV has a much wider aspect ratio of 16:9 instead of 4:3. b)HDTV moves toward progressive (non-interlaced) scan. The rationale is that interlacing introduces serrated edges to moving objects and flickers along horizontal edges. 33Li, Drew, Liu

34. Fundamentals of Multimedia 2 nd ed., Chapter 5 The services provided include: -SDTV (Standard Definition TV): the NTSC TV or higher. -EDTV (Enhanced Definition TV): 480 active lines or higher, i.e., the third and fourth rows in Table 5.4. -HDTV (High Definition TV): 720 active lines or higher. So far, the popular choices are: 720P (1,280×720, progressive scan, 30 fps) 1080I (1,920 × 1,080, interlaced, 30 fps) 1080P (1,920 × 1,080, progressive scan, 30 or 60 fps). 34Li, Drew, Liu

35. Fundamentals of Multimedia 2 nd ed., Chapter 5 5.2.4 Ultra High Definition TV (UHDTV) UHDTV is a new generation of HDTV. The standards announced in 2012 support 4K UHDTV: 2160P (3,840×2,160, progressive scan) and 8K UHDTV: 4320P (7,680×4,320, progressive scan). The aspect ratio is 16:9. The bit-depth can be up to 12 bits, and the chroma subsampling can be 4:2:0 or 4:2:2. The supported frame rate has been gradually increased to 120 fps. The UHDTV will provide superior picture quality, comparable to IMAX movies, but it will require a much higher bandwidth and bitrate. Li, Drew, Liu35

36. Fundamentals of Multimedia 2 nd ed., Chapter 5 5.3 Video Display Interfaces 36Li, Drew, Liu Fig. 5.7: Connectors for typical analog display interfaces. From left to right: Component video, Composite video, S- video, and VGA. 5.3.1 Analog Display Interfaces Analog video signals are often transmitted in one of three different interfaces: Component video, Composite video, and S-video. Figure 5.7 shows the typical connectors for them.

37. Fundamentals of Multimedia 2 nd ed., Chapter 5 Component video Component video: Higher-end video systems make use of three separate video signals for the red, green, and blue image planes. Each color channel is sent as a separate video signal. a)Most computer systems use Component Video, with separate signals for R, G, and B signals. b)For any color separation scheme, Component Video gives the best color reproduction since there is no “crosstalk” between the three channels. c)This is not the case for S-Video or Composite Video, discussed next. Component video, however, requires more bandwidth and good synchronization of the three components. 37Li, Drew, Liu

38. Fundamentals of Multimedia 2 nd ed., Chapter 5 Composite Video Composite video: color (“chrominance”) and intensity (“luminance”) signals are mixed into a single carrier wave. a)Chrominance is a composition of two color components (I and Q, or U and V). b)In NTSC TV, e.g., I and Q are combined into a chroma signal, and a color subcarrier is then employed to put the chroma signal at the high-frequency end of the signal shared with the luminance signal. 38Li, Drew, Liu

39. Fundamentals of Multimedia 2 nd ed., Chapter 5 a)The chrominance and luminance components can be separated at the receiver end and then the two color components can be further recovered. b)When connecting to TVs or VCRs, Composite Video uses only one wire and video color signals are mixed, not sent separately. The audio and sync signals are additions to this one signal. Since color and intensity are wrapped into the same signal, some interference between the luminance and chrominance signals is inevitable. Li, Drew, Liu39

40. Fundamentals of Multimedia 2 nd ed., Chapter 5 S-Video S-Video: as a compromise, (separated video, or Super-video, e.g., in S-VHS) uses two wires, one for luminance and another for a composite chrominance signal. Less crosstalk between the color information and the crucial gray- scale information. The reason for placing luminance into its own part of the signal is that black-and-white information is most crucial for visual perception. – Humans are able to differentiate spatial resolution in grayscale images with a much higher acuity than for the color part of color images. – As a result, we can send less accurate color information than must be sent for intensity information — we can only see fairly large blobs of color, so it makes sense to send less color detail. 40Li, Drew, Liu

41. Fundamentals of Multimedia 2 nd ed., Chapter 5 5.3.2 Digital Display Interfaces Fig. 5.8: Connectors of different digital display interfaces. From left to right: DVI, HDMI, DisplayPort. Li, Drew, Liu41 Digital interfaces emerged in 1980s (e.g., Color Graphics Adapter (CGA)), and evolved rapidly. Today, the most widely used digital video interfaces include Digital Visual Interface (DVI), High-Definition Multimedia Interface (HDMI), and DisplayPort.

42. Fundamentals of Multimedia 2 nd ed., Chapter 5 High-Definition Multimedia Interface (HDMI) HDMI is a newer digital audio/video interface developed to be backward compatible with DVI. 1.HDMI doesn’t carry analog signal and hence is not compatible with VGA. 2.HDMI supports both RGB and YCbCr 4:4:4 or 4:2:2. [DVI is limited to the RGB color range (0-255). ] 3.HDMI supports digital audio, in addition to digital video. The maximum pixel clock rate for HDMI 1.0 is 165 MHz, which is sufficient to support 1080P (1,920 × 1,200) at 60 Hz. HDMI 2.0 was released in 2013, which supports 4K resolution at 60 frames per second. Li, Drew, Liu42

43. Fundamentals of Multimedia 2 nd ed., Chapter 5 5.4 3D Video and TV Three-dimensional (3D) pictures and movies have been in existence for decades. The rapid progress in R&D of 3D technology and the success of the 2009 film Avatar have pushed 3D video to its peak. Increasingly, it is in movie theaters, broadcast TV (e.g., sporting events), PCs, and various hand-held devices. The main advantage of the 3D video is that it enables the experience of immersion — be there, and really Be there! Li, Drew, Liu43

44. Fundamentals of Multimedia 2 nd ed., Chapter 5 5.4.1 Cues for 3D Percept Monocular Cues: Shading, Perspective scaling, Relative size, Texture gradient, Blur gradient, Haze, Occlusion, Motion parallax. Among the above monocular cues, it is said that Occlusion and Motion parallax are more effective. Li, Drew, Liu44

45. Fundamentals of Multimedia 2 nd ed., Chapter 5 Binocular Cues: The human vision system uses binocular vision, i.e., stereo vision, aka. Stereopsis. Our left and right eyes are separated by a small distance, on average approximately two and half inches, or 65 mm. This is known as the interocular distance. The left and right eyes have slightly different views. The amount of the shift, or disparity, is dependent on the object’s distance from the eyes, i.e., its depth, thus providing the binocular cue for the 3D percept. Current 3D video/TV systems are almost all based on stereopsis because it is believed to be the most effective cue. Li, Drew, Liu45

46. Fundamentals of Multimedia 2 nd ed., Chapter 5 5.4.2 3D Camera Models Simple Stereo Camera Model: The left and right cameras are identical (same lens, same focal length, etc.). The cameras’ optical axes are in parallel, pointing at the Z-direction, the scene depth. where f is the focal length, b is the length of the baseline,, is the disparity or horizontal parallax. Zero disparity for objects at the infinity. Li, Drew, Liu46

47. Fundamentals of Multimedia 2 nd ed., Chapter 5 Toed-in Stereo Camera Model: Similar to human vision system When humans focus on an object at a certain distance, our eyes rotate around a vertical axis in opposite directions in order to obtain (or maintain) single binocular vision ─ the so-called vergence. Disparity d = 0 at the object of focus, and at the locations that have the same distance from the observer as the object of focus. d > 0 for objects farther than the object of focus (the so-called positive parallax). d < 0 for nearer objects (negative parallax). Li, Drew, Liu47

48. Fundamentals of Multimedia 2 nd ed., Chapter 5 5.4.3 3D Movie and TV Based on Stereo Vision 3D Movie Using Colored Glasses: glasses tinted with complementary colors, usually red on the left and cyan on the right ─ Anaglyph 3D. 3D Movie Using Circularly Polarized Glasses: polarized glasses that the audience wears allows one of the two polarized pictures to pass through while blocking the other, e.g., in the RealD cinemas. 3D TV with Shutter Glasses: the liquid crystal layer on the glasses becomes opaque (behaving like a shutter) when some voltage is applied. The glasses are actively (e.g., via Infra-Red) synchronized with the TV set that alternately shows left and right images in a Time Sequential manner. Li, Drew, Liu48

49. Fundamentals of Multimedia 2 nd ed., Chapter 5 5.4.4 The Vergence-Accommodation Conflict Accommodation ─ to maintain a clear (focused) image on an object when its distance changes. As in Figure 5.9(a), in human vision, normally, Focal distance = Vergence distance. As in Figure 5.9(b), most 3D video/movie/TV viewing requires Focal distance ≠ Vergence distance. This creates the Vergence-Accommodation Conflict ─ one of the main reasons for eye fatigue and strain while viewing 3D video/TV/movie. Li, Drew, Liu49

50. Fundamentals of Multimedia 2 nd ed., Chapter 5 Fig. 5.9: The Vergence-Accommodation Conflict. Li, Drew, Liu50

51. Fundamentals of Multimedia 2 nd ed., Chapter 5 5.4.5 Autostereoscopic (Glasses-Free) Display Devices Parallax Barrier ─ a layer of opaque material with slits is placed in front of the normal display device, e.g., an LCD. See Fig. 5.10(a). Used in e.g., Nintendo 3DS, Fujifilm 3D camera, and Toshiba’s glasses-free 3D TV. Lenticular Lens ─ Instead of barriers, columns of magnifying lenses can be placed in front of the display to direct lights properly to the left and right eyes. See Fig. 5.10(b). Integral Imaging ─ Instead of cylindrical lenses as shown above, an array of spherical convex microlenses can be used to generate a large number of distinct micro-images. It enables the rendering of multiple views from any directions. Li, Drew, Liu51

52. Fundamentals of Multimedia 2 nd ed., Chapter 5 Fig. 5.10: Autostereoscopic Display Devices. Li, Drew, Liu52

53. Fundamentals of Multimedia 2 nd ed., Chapter 5 5.4.6 Disparity Manipulation in 3D Content Creation Disparity Range — map (often suppress) the original disparities into the range that will fit in the comfort zone of most viewers. Disparity Sensitivity — human vision is more capable of discriminating different depths when they are nearby, so do nonlinear disparity mapping (suppress the far range). Disparity Gradient — human vision has a limit of disparity gradient in binocular fusion, so avoid it in depth editing. Disparity Velocity — we cannot rapidly process large accommodation and vergence changes (i.e., disparity changes), so slow it down! Li, Drew, Liu53